The present invention relates to a solid electrolytic capacitor and a production method thereof. More specifically, the present invention relates to a solution of an oxidizing agent (an oxidizing agent solution) and a solution of a monomer (a monomer solution) necessary for forming a solid electrolyte of the solid electrolytic capacitor. The present invention further relates to a solid electrolytic capacitor or a production method thereof, comprising preferably a solid electrolyte formed of an electrically conducting polymer composition obtained by specifying the viscosity of the oxidizing agent solution or the monomer solution.
The present invention even further relates to a solid electrolytic capacitor and a production method thereof, preferably comprising a solid electrolyte formed of an electroconducting (electrically conducting) polymer composition obtained by specifying the humidity in the polymerization of an oxidizing agent solution and a monomer solution in the solid electrolyte.
The present invention even further relates to a solid electrolytic capacitor, more specifically, a solid electrolytic capacitor in which the solid electrolyte formed on the outer surface of an anode body is an electrically conducting polymer containing a lamellar structure, wherein the solid electrolyte provided on the dielectric film formed on a valve acting metal occupies from 10 to 95% of the space within a pore of the electrode, so that the adhesive property between the solid electrolyte and the dielectric layer formed on a metal oxide film can be improved, high capacitance and low impedance can be realized, the leakage current can be improved, and good moisture resistance load characteristics and excellent heat resistance can be achieved.
The present invention also relates to a solid electrolytic capacitor, more specifically, a solid electrolytic capacitor in which the solid electrolyte formed on the outer surface of an anode body is an electrically conducting polymer containing a lamellar structure, wherein the solid electrolyte provided on the dielectric film formed on a valve acting metal covers 60% or more of the dielectric film, so that the adhesive property between the solid electrolyte and the dielectric layer formed on a metal oxide film can be improved, high capacitance and low impedance can be realized, and good moisture resistance load characteristics and excellent heat resistance can be achieved.
A solid electrolytic capacitor is a device where an oxide dielectric film is formed on the surface of an anode substrate comprising a metal foil subjected to etching treatment or the like, a solid semiconductor layer (hereinafter referred to as a xe2x80x9csolid electrolytexe2x80x9d) is formed as a counter electrode outside the dielectric layer, and an electrically conducting layer such as an electrically conducting paste is further formed thereon. The device is actually used as a product after completely sealing the entire device with epoxy resin or the like and leading out terminals from respective electrodes.
In recent years, with the progress toward digitized electrical equipment or personal computers capable of high speed processing, demands are increasing for a compact capacitor having a large capacitance or a capacitor showing low impedance in the high frequency region. As the compact capacitor having a large capacitance, electrolytic capacitors such as aluminum electrolytic capacitor and tantalum electrolytic capacitor are known. The aluminum electrolytic capacitor can be advantageously produced to have a large capacitance at a low cost but has a problem in that when an ion conducting liquid electrolyte is used as the electrolyte, high impedance results in the high frequency region and the capacitance decreases accompanying the evaporation of electrolytic solution with the elapse of time, and in addition, the temperature characteristics are bad. The tantalum electrolytic capacitor has a problem in that a manganese oxide is generally used as the electrolyte and since this manganese oxide is mainly produced by the thermal decomposition of manganese nitrate, the possibility of damage of the dielectric film at the thermal decomposition cannot be eliminated, and moreover, due to relatively high specific resistance of manganese oxide, the impedance is high in the high frequency region.
For the solid electrolyte, it is already known to use, for example, an inorganic semiconductor material such as manganese dioxide and lead dioxide, a TCNQ complex salt, an intrinsic electrically conducting polymer having an electric conductivity of from 10xe2x88x923 to 5xc3x97103 S/cm (JP-A-1-169914 (the term xe2x80x9cJP-Axe2x80x9d as used herein means an xe2x80x9cunexamined published Japanese patent applicationxe2x80x9d , corresponding to U.S. Pat. No. 4,803,596)) or an electrically conducting polymer such as xcfx80-conjugated polyaniline (see, JP-A-61-239617), polypyrrole (see, JP-A-61-240625), polythiophene derivative (see, JP-A-2-15611) or polyisothianaphthene (see, JP-A-62-118511). These electrically conducting polymers comprising a xcfx80-conjugated structure are mostly used as a composition containing a dopant. In recent years, not only the addition of a dopant but also a combination use with, for example, manganese dioxide (see, JP-B-6-101418 (the term xe2x80x9cJP-Bxe2x80x9d as used herein means an xe2x80x9cexamined Japanese patent publicationxe2x80x9d) (corresponding to U.S. Pat. No. 4,959,753)) or filler (see, JP-A-9-320901) is employed.
In the case of using lead dioxide, precautions as to the environment are additionally required.
Capacitors using a TCNQ complex salt solid for the solid electrolyte have good heat fusion workability and excellent electric conductivity but are considered to show poor reliability in heat resistance (soldering heat resistance) at the solder joining because the TCNQ complex salt itself has a problem in heat resistance.
Capacitors using an electrically conducting polymer for the solid electrolyte do not have a dielectric film rupture problem and favored with a high impedance property but disadvantageously are deficient in heat resistance, thermal shock resistance and vibration resistance.
The electrically conducting polymer layer as a solid electrolyte has a high electric conductivity and is formed to cover throughout the inner surfaces of pores inside the cathode. At this time, for satisfying the fundamental characteristics of the capacitor, such as leakage current and heat resistance, the structure formed inside the foil pore and the coverage must be considered.
An example of the electrically conducting polymer formed article of which the structure is controlled is a sponge-like electrically conducting polymer formed article having a continuous phase of an electrically conducting polymer disclosed in JP-A-8-53566. This formed article is produced by a method of cooling a solvent-containing polyaniline or derivative thereof in any molding container to freeze the solvent and then removing the solvent, or a method of cooling a solution containing aniline or an aniline derivative as a monomer and a protonic acid/oxidizing agent to freeze the solvent and polymerizing the solution at a temperature lower than the melting point of the solvent.
In particular, as regarding the solid electrolyte provided on a dielectric film formed on a valve acting metal which is a constituent element of a capacitor, JP-A-7-122464 refers to a structure of an electrically conducting polymer formed within a microfine pore and discloses a tantalum solid electrolytic capacitor comprising a sintered body of tantalum powder, an oxide dielectric film formed on the surface of the sintered body and as a solid electrolyte, an electrically conducting polymer compound covering the oxide dielectric film. The tantalum solid electrolytic capacitor disclosed in this patent publication is constructed such that the electrically conducting polymer compound covers the oxide dielectric film while leaving a cavity in a pore constituting the surface of a sintered body and the electrically conducting polymer compound occupies, in terms of the volume ratio, 70% or less of the volume of the pore.
However, JP-A-8-53566 does not disclose an application example of the sponge-like electrically conducting polymer formed article as to a solid electrolytic capacitor. According to the production method disclosed in this patent publication, the sponge-like electrically conducting polymer formed article is produced by cooling an electrically conducting polymer solution to freeze the solvent, polymerizing the solution and then removing the solvent by freeze-drying or melting it. This method has a problem as to operativity and moreover, the oxide dielectric film is readily damaged on freezing or melting. Therefore, it is difficult to apply this technique to a solid electrolytic capacitor.
In the method disclosed in JP-A-7-122464 of forming a structure such that an electrically conducting polymer compound covers an oxide dielectric film while leaving a cavity in the pore, the ratio of the cavity occupying the pore is controlled by the repetition of oxidation polymerization. Therefore, if an electrically conducting polymer layer is formed to have a large thickness on the outer surface of an anode body after forming the electrically conducting polymer while leaving a cavity in the pore, the cavity already present in the microfine pore is clogged. Thus, an electrically conducting polymer layer cannot be formed to have a predetermined thickness on the outer surface while maintaining the cavity in a microfine pore. Furthermore, the surface of the polymer layer is not uneven, therefore, the adhesion to the electrically conducting paste layer is poor. Moreover, the ratio of the electrically conducting polymer compound as a solid electrolyte is specified only by volume. This patent publication does not refer at all to the covering area which relates to adhesion (which is an important factor governing capacitor properties) between the dielectric film and the electrically conducting polymer as a solid electrolyte.
As such, in regard of a solid electrolytic capacitor where an electrolytic conducting polymer to work out to a solid electrolyte is formed on a dielectric film of a solid electrolytic capacitor electrode foil comprising a valve acting metal having formed thereon an oxide film, no technique has been heretofore known on the optimal ratio in covering the dielectric film with the polymer.
As the oxidizing agent for use in conventional techniques, for example, chemical polymerization of 5-membered heterocyclic compounds such as thiophene, iron(III) chloride, Fe(ClO4)3, organic acid iron(III) salt, inorganic acid iron(III) salt, alkyl persulfate, ammonium persulfate (hereinafter simply referred to as xe2x80x9cAPSxe2x80x9d), hydrogen peroxide, K2Cr2O7, etc., (see, JP-A-2-15611), cupric compounds, silver compounds, etc., (see, JP-A-10-32145) are known.
With respect to the method for forming a solid electrolyte using an electrically conducting polymer, for example, a method of fusing the electrically conducting polymer (solid electrolyte) described above on a dielectric film on the surface of a valve-acting metal having fine void structures to form an electrically conducting polymer layer, and a method of depositing the above-described electrically conducting polymer on a dielectric film are known.
More specifically, in the case of using, for example, a polymer of a 5-membered heterocyclic compound such as pyrrole or thiophene for the solid electrolyte, a method of dipping an anode foil having formed thereon a dielectric film in a lower alcohol and/or water-based solution of a 5-membered heterocyclic compound monomer and after removing it, again dipping the foil in an aqueous solution having dissolved therein an oxidizing agent and an electrolyte to cause chemical polymerization of the monomer, thereby forming an electrically conducting polymer layer (see, JP-A-5-175082), a method of coating simultaneously or sequentially a 3,4-ethylenedioxythiophene monomer and an oxidizing agent each preferably in the form of a solution on the oxide film of a metal foil to form an electrically conducting polymer layer (see, JP-A-2-15611 and JP-A-10-32145), and the like are known.
In order to solve the above-described problems, the electrically conducting polymer such as polypyrrole is formed by electrolytic or chemical polymerization and used for the solid electrolyte of a solid electrolytic capacitor. However, the electrically conducting polymer film obtained fails to have sufficiently high uniformity or when the electrolytic capacitor is fabricated, the soldering heat resistance, the impedance property and the like are not satisfactory.
In recent years, a method of forming an electrically conducting polymer, particularly polypyrrole, is disclosed, where a methanol solution of dodecylbenzenesulfonic acid iron salt used as an oxidizing agent for causing chemical oxidation polymerization is specified to have a viscosity of less than 100 cp by taking account of production efficiency (see, JP-A-4-94110). However, in this technique, thiophene, aniline and derivatives thereof are not described and the oxidizing agent used is a metal salt of an organic acid. Therefore, the viscosity inevitably increases in the process for obtaining a concentration effective in the polymerization.
Also, a method for forming an electrically conducting polymer, particularly polypyrrole, is disclosed, where the viscosity of the oxidizing agent using an aromatic sulfonic acid metal salt is from 100 to 500 cp and thereby the repetition frequency of dipping in an oxidizing agent solution and in a monomer solution is decreased (see, JP-A-10-14954). When the viscosity of the oxidizing agent is reduced to 100 cp or less, the polymerization efficiency of the monomer in turn decreases, as a result, the amount of the electrically conducting polymer formed is disadvantageously small.
Recently, also a method of forming an electroconducting polymer by chemical oxidative polymerization is known, where an isopropyl alcohol mixed solution containing 3,4-ethylenedioxythiophene as a monomer and ferric p-toluenesulfonate as an oxidizing agent is allowed to stand in an air at a temperature of from about 30xc2x0 C. to about 50xc2x0 C. and a humidity of about 60% or more for about 30 minutes (see, JP-A-10-64761).
However, because of the formation into a mixed solution of monomer, oxidizing agent and isopropyl alcohol, the monomer and the oxidizing agent are difficult to recover and the yield of products decreases. Furthermore, the mixed solution readily evaporates due to the isopropyl alcohol used. As a result, the polymerization reaction is accelerated and the polymer thus formed at a high rate is duly considered to have very coarse form. For obtaining a polymer form capable of exhibiting sufficiently high electric conductivity, the humidity condition of about 60% or more seems to be necessary as water content in the atmosphere.
An object of the present invention is to provide a solid electrolytic capacitor having excellent properties satisfying the requirements with respect to compact size, reduction in weight, high capacitance, high frequency property, tan xcex4 (tangent of loss angle), leakage current, heat resistance (reflow soldering property), durability and the like.
In particular, an object of the present invention is to provide a heat resistant solid electrolytic capacitor having excellent low impedance property and high durability in a sparking voltage test using an electrically conducting polymer obtained by specifying the viscosity of an oxidizing agent solution and/or a monomer solution.
First, increase in viscosity of an oxidizing agent solution and/or a monomer solution causes a reduction in capacitance.
More specifically, an aluminum foil having formed thereon a dielectric material obtained by etching the surface is dipped with an oxidizing agent solution or a monomer solution and then dried, as a result, a highly viscous oxidizing agent or monomer film is formed on the surface of a porous body, and microfine pore openings present on the surface of the porous body are clogged. The polymer is formed on the surface by contact with a monomer or an oxidizing agent, therefore, the polymer is not formed inside the pores, which causes a reduction in capacitance.
Second, a decrease in the viscosity of an oxidizing agent solution and/or a monomer solution causes reduction in the amount of polymer adhered in a single polymerization step. Therefore, a satisfactory solid electrolyte may not be formed unless the number of polymerization steps is increased. That is, the decrease in viscosity of an oxidizing agent solution and/or a monomer solution abates capability of oxidizing the monomer, lessens the amount of monomer, and reduces the amount of polymer formed.
Under these circumstances, it is necessary to obtain capacitor properties with a small number of polymerization steps to allow an oxidizing agent solution and/or a monomer solution to have a viscosity of a certain level and to increase the capacitance.
An object of the present invention is to provide a method for producing a solid electrolyte capable of achieving appearance of capacitor properties with a reduced dipping frequency in an oxidizing agent solution and in a monomer solution, where the viscosity of an oxidizing agent solution and/or a monomer solution used for forming a solid electrolyte of a solid electrolytic capacitor from an electrically conducting polymer is specified and thereby the monomer oxidation efficiency is increased.
In particular, a further object of the present invention is to provide a solid electrolytic capacitor having small leakage current and excellent tan xcex4 by using an electroconducting polymer obtained by specifying the humidity in the polymerization process.
The mixed solution of a monomer and an oxidizing agent has a problem in the humidity control and yield during the polymerization process.
This is ascribable to the fact that in the case of impregnating a dielectric film obtained by etching the surface of a valve-acting metal with a mixed solution of a monomer and an oxidizing agent and polymerizing it at a low humidity, a highly viscous film is formed on the surface of the porous body due to the presence of a monomer and an oxidizing agent dispersed together. As a result, microfine pore inlets present on the surface of porous body are blocked and the polymer cannot be satisfactorily formed in the inside of pores, which causes reduction in the capacitance. Accordingly, in this embodiment the humidity must be controlled to about 60% or more as a polymerization condition.
Furthermore, the polymerization proceeds on aging due to the presence of a monomer and an oxidizing agent together, as a result, the oligomer ratio increases, the mixed solution itself polymerizes, the monomer and the oxidizing agent cannot be recovered, and the yield decreases.
Even in the case of forming an electroconducting polymer composition film by repeatedly coating a solution containing a monomer of the polymer and a solution containing an oxidizing agent one after another, the humidity in the polymerization process must also be controlled so as to ensure high electric conductivity and high reliability.
This is because if the humidity is excessively high in the polymerization process, the polymerization slowly proceeds and the yield of polymer decreases, whereas if the humidity is excessively low, the adhered water and the monomer evaporate and the yield of polymer decreases.
Accordingly, also an object of the present invention is to provide a method for producing a solid electrolyte capable of achieving appearance of good capacitor properties by specifying the humidity range in the polymerization process for forming a solid electrolyte of a solid electrolytic capacitor using an electroconducting polymer, and thereby increasing the oxidation efficiency of monomer.
In order to attain the above-described objects, extensive investigations have been made on the oxidizing agent solution and/or the monomer solution necessary for the electrically conducting polymer composition forming the solid electrolyte. As a result, it has been found that a compact and high-performance solid electrolytic capacitor having low impedance and high durability in a sparking voltage test can be obtained by a solid electrolytic capacitor comprising counter electrodes with one party electrode being assigned a microfine structure dielectric film comprising a metal oxide on the surface of a valve-acting metal foil, and a solid electrolyte comprising an electrically conducting polymer composition formed on the dielectric film, where the electrically conducting polymer forming the solid electrolyte is formed from an oxidizing agent solution and/or a monomer solution having a viscosity of less than 100 cp. An embodiment of the present invention has been accomplished based on this finding.
It has also been found that a compact and high-performance solid electrolytic capacitor having small leakage current and excellent tan xcex4 can be obtained when in a solid electrolytic capacitor comprising counter electrodes with one part electrode being assigned to a microfine structure dielectric film comprising a metal oxide on the surface of a valve-acting metal foil, and a solid electrolyte comprising an electroconducting polymer composition formed on the dielectric film, the solid electrolyte is an electroconducting polymer produced by the polymerization in a humidity atmosphere of from 10% to less than 60%. Another embodiment of the present invention has been accomplished based on this finding.
As a result of additional investigations to solve the above-described problems, the present inventors have first found that in a solid electrolytic capacitor, more specifically, in a solid electrolytic capacitor where the solid electrolyte on the outer surface of an anode body is an electrically conducting polymer containing a lamellar structure, when the solid electrolyte is provided on the dielectric film formed on a valve acting metal, to occupy from 10 to 95% of the space within a pore of the electrode, the solid electrolytic capacitor obtained has improved adhesion between the solid electrolyte and the dielectric film formed on the valve acting metal and favored with excellent stability of various fundamental properties such as capacitance and dielectric loss (tan xcex4), and stability of reflow soldering heat resistance and moisture resistance load characteristics.
Furthermore, as a result of extensive investigations to solve the above-described problems, the present inventors have also found that in a solid capacitor, more specifically, in a solid electrolytic capacitor where the solid electrolyte is an electrically conducting polymer containing a lamellar structure, when the solid electrolyte is provided on a dielectric film formed on a valve acting metal, to cover 60% or more of the dielectric film, the solid electrolytic capacitor obtained is favored with excellent stability of various fundamental properties such as capacitance and dielectric loss (tan xcex4), and stability of reflow soldering heat resistance and moisture resistance load characteristics. A further embodiment of the present invention has been accomplished based on these findings.
More specifically, objects of the present invention has been attained by the following embodiments:
(1) a method for producing a solid electrolytic capacitor, comprising covering a valve-acting metal anode foil having formed on the surface thereof an oxide dielectric film with a repeating sequence of a solution containing a monomer of an electrically conducting polymer and a solution containing an oxidizing agent to form an electrically conducting polymer composition film on the dielectric film, wherein the solution containing a monomer of an electrically conducting polymer and/or the solution containing an oxidizing agent has a viscosity of less than 100 cp;
(2) a solid electrolytic capacitor comprising an oxide dielectric film having thereon an electrically conducting polymer composition layer, which is produced by the method described in (1) above, wherein the electrically conducting polymer in the composition contains as a repeating chemical structure a structural unit represented by the following formula (1a): 
wherein the substituents R1 and R2 each independently represents a monovalent group selected from the group consisting of a hydrogen atom, a linear or branched, saturated or unsaturated hydrocarbon group having from 1 to 6 carbon atoms, a linear or branched, saturated or unsaturated alkoxy group having from 1 to 6 carbon atoms, a hydroxyl group, a halogen atom, a nitro group, a cyano group, a trifluoromethyl group, a phenyl group and a substituted phenyl group; R1 and R2 may be combined with each other at an arbitrary position to form at least one divalent chain for forming at least one 5-, 6- or 7-membered saturated or unsaturated ring structure; Xa represents a hetero atom selected from the group consisting of S, O, Se or Te; the alkyl group and the alkoxy group represented by R1 or R2 each may optionally contain in the chain thereof a carbonyl bond, an ether bond, an ester bond, an amide bond or an imino bond; and xcex4 represents a number of from 0 to 1;
(3) the solid electrolytic capacitor as described in (2) above, wherein the structural unit represented by formula (1a) is a chemical structure represented by the following formula (2): 
wherein the substituents R4 and R5 each independently represents a hydrogen atom, a linear or branched, saturated or unsaturated hydrocarbon group having from 1 to 6 carbon atoms, or a substituent for forming at least one 5-, 6- or 7-membered saturated or unsaturated ring structure containing the two oxygen elements shown in the formula by combining hydrocarbon groups having from 1 to 6 carbon atoms with each other at an arbitrary position; the ring structure formed as described above includes a chemical structure such as a substituted vinylene group and a substituted o-phenylene group; and xcex4 represents a number of from 0 to 1;
(4) the method for producing a solid electrolytic capacitor as described in (1) above, comprising an oxide dielectric film having provided thereon an electrically conducting polymer composition layer, the method comprising polymerizing a monomer compound on an oxide dielectric film by an oxidizing agent, wherein the monomer compound is a compound represented by the following formula (3a): 
wherein the substituents R1, R2 and Xa are the same as defined in formula (1a) and the polymerization is performed in the presence of a compound capable of providing an anion of an organic sulfonic acid compound or sulfonate anion having a doping ability;
(5) the method for producing a solid electrolytic capacitor as described in (4) above, wherein the monomer compound represented by formula (1a) is a compound represented by the following formula (4): 
wherein the substituents R4 and R5 are the same as defined in formula (2);
(6) the method for producing a solid electrolytic capacitor as described in (1), (4) and (5) above, wherein the oxidizing agent is a metal salt solution of an oxidative inorganic acid;
(7) the method for producing a solid electrolytic capacitor as described in (1), (4), (5) and (6) above, wherein the metal salt of an oxidative inorganic acid is a persulfate;
(8) the method for producing a solid electrolytic capacitor as described in (1), (4), (5), (6) and (7) above, wherein the monomer compound is a monomer compound of a polymer having electric conductivity, and thiophene, aniline or derivatives thereof;
(9) the method for producing a solid electrolytic capacitor as described in (1), (4), (5), (6), (7) and (8) above, wherein the thiophene derivative is 3,4-ethylenedioxythiophene;
(10) a method for producing a solid electrolytic capacitor, comprising a polymerization step of coating a solution containing a monomer of an electroconducting polymer and a solution containing an oxidizing agent in repeating sequence on a valve-acting metal anode having formed on the surface thereof an oxide dielectric film, wherein the electroconducting polymer is formed by setting the humidity in the atmosphere of polymerization process to from 10% to less than 60%;
(11) a solid electrolytic capacitor comprising an electroconducting polymer composition layer provided on the oxide dielectric film according to the method of (10) above, wherein the electroconducting polymer in the composition contains a structural unit represented by the following formula (1b) as a repeating chemical structure: 
wherein the substituents R1 and R2 each independently represents a monovalent group selected from the group consisting of a hydrogen atom, a linear or branched, saturated or unsaturated hydrocarbon group having from 1 to 6 carbon atoms, a linear or branched, saturated or unsaturated alkoxy group having from 1 to 6 carbon atoms, a hydroxyl group, a halogen atom, a nitro group, a cyano group, a linear or branched perfluoroalkyl group having from 1 to 6 carbon atoms, a phenyl group and a substituted phenyl group; the substituents R1 and R2 may be combined with each other at an arbitrary position to form at least one divalent chain for forming at least one 5-, 6- or 7-membered saturated or unsaturated ring structure; Xb represents a hetero atom selected from S, O, Se, Te and NR3; R3 represents a hydrogen atom, a linear or branched, saturated or unsaturated hydrocarbon group having from 1 to 6 carbon atoms, a phenyl group, or a linear or branched, saturated or unsaturated alkoxy group having from 1 to 6 carbon atoms; and the alkyl group and the alkoxy group represented by R1, R2 or R3 each may optionally contain in the chain thereof a carbonyl bond, an ether bond, an ester bond, an amide bond or an imino bond; provided that xcex4 is a number of from 0 to 1;
(12) the solid electrolytic capacitor as described in (11) above, wherein the structural unit represented by formula (1b) is a chemical structure represented by the following formula (2): 
wherein the substituents R4 and R5 each independently represents a hydrogen atom, a linear or branched, saturated or unsaturated hydrocarbon group having from 1 to 6 carbon atoms or a substituent forming at least one 5-, 6- or 7-membered saturated or unsaturated ring structure containing the two oxygen atoms shown in the formula when the hydrocarbon groups having from 1 to 6 carbon atoms are combined with each other at an arbitrary position, the ring structure formed including a chemical structure such as a substituted vinylene group and a substituted o-phenylene group, and xcex4 represents a number of from 0 to 1;
(13) the method for producing a solid electrolytic capacitor as described in (10) above, the solid electrolytic capacitor comprising an electroconducting polymer composition layer provided on the oxide dielectric film, wherein a monomer is polymerized on the oxide dielectric film by an oxidizing agent, the monomer is a compound represented by the following formula (3b): 
wherein the substituents R1, R2 and Xb are the same as defined in formula (1b), and the polymerization is performed in the presence of a compound capable of providing an anion of an organic sulfonic acid or sulfonate anion having a doping ability;
(14) the method for producing a solid electrolytic capacitor as described in (13) above, wherein the monomer represented by formula (1b) is a compound represented by the following formula (4): 
wherein the substituents R4 and R5 are the same as defined in formula (2);
(15) the method for producing a solid electrolytic capacitor as described in (11) and (14) above, wherein the oxidizing agent is a metal salt or ammonium salt solution of an oxidative inorganic acid;
(16) the method for producing a solid electrolytic capacitor as described in (11), (14) and (15) above, wherein the metal salt or ammonium salt of an oxidative inorganic acid is persulfate;
(17) the method for producing a solid electrolytic capacitor as described in (11), (14), (15) and (16) above, wherein the monomer is a monomer for a polymer having electric conductivity, and pyrrole, thiophene, aniline or a derivative thereof;
(18) the method for producing a solid electrolytic capacitor as described in (11), (14), (15), (16) and (17) above, wherein the thiophene derivative is 3,4-ethylenedioxythiophene;
(19) a solid electrolytic capacitor comprising a porous valve acting metal having formed thereon a dielectric film and a solid electrolyte formed on the dielectric film, wherein the solid electrolyte occupies from 10 to 95% of the space within a pore of the porous metal;
(20) the solid electrolytic capacitor as described in (19) above, wherein the solid electrolyte is an electrically conducting polymer containing a lamellar structure;
(21) a solid electrolytic capacitor comprising a porous valve acting metal having formed thereon a dielectric film and a solid electrolyte formed on the dielectric film, wherein the solid electrolyte covers 60% or more of the dielectric film;
(22) the solid electrolytic capacitor as described in (21) above, wherein the solid electrolyte is an electrically conducting polymer containing a lamellar structure;
(23) the solid electrolytic capacitor as described in (20) or (22) above, wherein at least a portion of an interlayer portion in said lamellar structure comprises a space portion;
(24) the solid electrolytic capacitor as described in any one of (19) to (23) above, wherein the space within a pore, partly occupied by the solid electrolyte, is an independent or communicated bubble void space;
(25) the solid electrolytic capacitor as described in any one of (19) to (24) above, wherein the solid electrolyte is an electrically conducting polymer containing as a repeating unit a divalent group comprising a 5-membered heterocyclic ring-containing compound or a derivative thereof;
(26) the solid electrolytic capacitor as described in (25) above, wherein the electrically conducting polymer containing as a repeating unit a divalent group comprising a 5-membered heterocyclic ring-containing compound or a derivative thereof is an electrically conducting polymer containing as a repeating unit a structure represented by the following formula (5): 
wherein the substituents R6 and R7 each independently represents a monovalent group selected from the group consisting of a hydrogen atom, a linear or branched, saturated or unsaturated hydrocarbon group having from 1 to 10 carbon atoms, an alkoxy group, an alkyl ester group, a halogen atom, a nitro group, a cyano group, a primary, secondary or tertiary amino group, CF3, a phenyl group and a substituted phenyl group, the hydrocarbon chains of R6 and R7 may be combined with each other at an arbitrary position to form at least one divalent chain for forming at least one 3-, 4-, 5-, 6- or 7-membered saturated or unsaturated hydrocarbon cyclic structure together with the carbon atoms substituted by R6 and R7, the cyclic combined chain may optionally contain a bond selected from the group consisting of carbonyl, ether, ester, amide, sulfide, sulfinyl, sulfonyl and imino, xcex4 is in the range of 0 to 1, Z represents an anion, and j represents the valency of Z and is 1 or 2;
(27) the solid electrolytic capacitor as described in (26) above, wherein the electrically conducting polymer has an electric conductivity of from 0.1 to 200 S/cm;
(28) the solid electrolytic capacitor as described in (19) to (27) above, wherein the valve acting metal is any one of aluminum, tantalum, niobium and titanium;
(29) a method for producing a solid electrolytic capacitor, comprising forming a dielectric film on a porous valve acting metal and forming a solid electrolyte on the dielectric film, wherein the solid electrolyte is formed to occupy from 10 to 95% of the space within a pore of the porous metal;
(30) a method for producing a solid electrolytic capacitor comprising forming a dielectric film on a porous valve acting metal and forming a solid electrolyte on the dielectric film, wherein the solid electrolyte is formed to cover about 60% or more of the dielectric film;
(31) a method for producing a solid electrolytic capacitor, comprising covering a valve-acting metal anode foil having formed on the surface thereof an oxide dielectric film with repeating sequence of a solution containing a monomer of an electrically conducting polymer and a solution containing an oxidizing agent and then polymerizing to form an electrically conducting polymer composition film on the dielectric film, wherein the solution containing a monomer of the electrically conducting polymer and/or the solution containing the oxidizing agent has a viscosity of less than about 100 cp at 23xc2x0 C.; wherein the electrically conducting polymer composition film is formed by setting the humidity in the atmosphere of the polymerization process to from about 10% to less than about 60%; and wherein the solid electrolyte is formed on the dielectric film to occupy from about 10 to about 95% of the space within a pore of the valve metal;
(32) a method for producing a solid electrolytic capacitor, comprising covering a valve-acting metal anode foil having formed on the surface thereof an oxide dielectric film with repeating sequence of a solution containing a monomer of an electrically conducting polymer and a solution containing an oxidizing agent and then polymerizing to form an electrically conducting polymer composition film on the dielectric film, wherein the solution containing a monomer of the electrically conducting polymer and/or the solution containing the oxidizing agent has a viscosity of less than about 100 cp at 23xc2x0 C.; wherein the electrically conducting polymer composition film is formed by setting the humidity in the atmosphere of the polymerization process to from about 10% to less than about 60%; and wherein the solid electrolyte is formed on the dielectric film to cover about 60% or more of said dielectric film;
(33) a solid electrolytic capacitor produced by the process of embodiment (31); and
(34) a solid electrolytic capacitor produced by the process of embodiment (32).